FM10K_RX_DESC
union fm10k_rx_desc *rxd = FM10K_RX_DESC(ring, i);
rx_desc = FM10K_RX_DESC(rx_ring, i);
rx_desc = FM10K_RX_DESC(rx_ring, 0);
prefetch(FM10K_RX_DESC(rx_ring, ntc));
rx_desc = FM10K_RX_DESC(rx_ring, rx_ring->next_to_clean);